An inverted front fork for bicycles and motorcycles includes an axle having non-circular ends that are clamped within corresponding non-circular dropout openings contained in the lower sections of the leg portions of the fork, thereby to increase the torsional stiffness of the fork.
It has been proposed to provide front forks for bicycles and motorcycles that are of the so-called xe2x80x9cinvertedxe2x80x9d or xe2x80x9cupside downxe2x80x9d type, wherein the outer cylindrical section of each of the telescopic legs of the fork is connected with the crown portion of the fork. As distinguished from conventional front forks as illustrated by the patents to Steward U.S. Pat. No. 5,833,259, Gonzalez U.S. Pat. No. 5,848,675 and Gonzalez, et al. U.S. Pat. No. 6,120,049, in the inverted front forks the conventional arch members connecting the upper ends of the lower telescopic sections of the leg portions of the fork are eliminated.
During the development and testing of such inverted front forks, it became apparent that the axle played a significant role in the torsional stiffness with this type of fork execution. Since the upside down design lacks the traditional brake arch or brace (which plays a critical role in the torsional performance), the upside down design requires the axle and clamping system to make up for any loss in torsional rigidity. In the prior art, various proposals have been presented for stabilizing the axle of the front fork of a cycle. In the Becker U.S. Pat. No. 5,984,423, it has been proposed to provide a wheel hub retaining device that contains a bore for receiving the skewer rod upon which the wheel is mounted, and a projecting portion shaped to fit securely within the dropout slot. Thus, the loads on the wheel are transferred to the interface between the hub and hub retainer rather than to the interface between the skewer rod and the dropout. Similarly, in the SUPERDUPERBUBBA suspension hub manufactured by Ringle Components Inc. of Trenton, N.J., it was proposed to shape the ends of the front fork axle with a D-shaped cross-sectional configuration corresponding to the dropout slot configuration, thereby to increase the stiffness of the entire fork/wheel system by turning the axle into a torsion bar. Pace Engineering of Great Britain has recently proposed an axle having non-circular end portions adapted for insertion within the dropout slots contained in the lower extremities of the legs of a front fork.
Applicant found that the traditional way of executing a thru axle design, which consist of a round axle that goes xe2x80x9cthruxe2x80x9d the hub and is pinched at the fork dropouts, was not adequate. It did not give the upside down design the torsional properties necessary for even acceptable performance. Prior proposals for stiffening the axle to fork connection included the use of an oversized axle dropout and hub system, which was significantly larger in diameter both through the hub and at the dropout clamping area. This was done not only to increase the strength and stiffness of the axle, but more importantly, to increase the punch area at the dropouts to create a stiffer junction. This system had many drawbacks, such as requiring a custom hub that would not accept the industry standard of 20 mm diameter axles through the hub. This would be costly due to the requirement for a custom hub or wheel configuration, make it unfriendly to consumers that already own wheels and as additional expense to the purchase of the fork. Also, for the purpose the axle serves, the 20 mm dimension is more than adequate. Furthermore, the larger hub, axle, and dropouts add unsprung weight over the 20 mm axle design, which is undesirable for the fork performance. Unsprung weight is weight that responds to the moment of the suspension action, and it is inertia that the fork has to overcome to respond to the terrain. The lighter the unsprung weight, the quicker the fork can respond to the terrain. It would potentially require a different disk brake rotor as most rotors are designed for the smaller hub flanges used in the 20 mm axle design. This would limit brake options and again add cost due to custom configurations. This oversize design would still not fully address the true problem, which is slippage/movement from the round axle at the dropout junction.
In order to avoid the above and other drawbacks of the known systems, the concept of using an axle shape that would lock the axle in the dropouts was developed, thereby eliminating the possibility of the axle having the opportunity to rotate in the dropout clamp. This would also put the axle into a true torsion spring situation, which would allow for further xe2x80x9ctuningxe2x80x9d of torsional stiffness by changing materials and thickness of axle. All of this while still using a 20 mm OD axle. It was decided to go with a hexagonal shape owing to advantages in manufacturability, installation, and durability. The same benefits, however, could be gained from numerous shapes, including square, oval, rectangular, etc. The results of the Hex Axle system were impressive. It reduced torsional deflection by half over the traditional 20 mm round clamping, and equaled or surpassed the oversize designs with a smaller, lighter, and more effective design. It was a major breakthrough that resulted in an upside down front fork design that surpasses the performance benchmark that was previously available.
Accordingly, a primary object of the present invention is to provide an inverted type front fork system for bicycles and motorcycles, including an axle the ends of which are non-circular and extend within corresponding non-circular dropout openings contained in the lower extremities of the leg portions of the fork.
A more specific object of the invention is to provide improved locking means for clamping the non-circular end portions of the axle within the corresponding dropout openings, respectively. In one embodiment, the locking means comprise clamping bolts that pinch together the bifurcated lower extremities of the fork legs, thereby to reduce the size of the non-circular dropout opening and to clamp the axle end to the associated leg. In a second embodiment, the non-circular axle end is locked within the associated dropout opening by quick-release means including a pivotally connected locking section that is operable by cam means to reduce the side of the dropout opening, thereby to clamp the axle end therein.
Another object of the invention is to provide an inverted fork assembly as described above including tension adjusting means for displacing the free ends of the legs together against stops carried by the axle, thereby to position the legs relative to the axle prior to clamping of the axle to the legs, whereby accurate positioning of the legs relative to the axle promotes an increase in the torsional stiffness of the inverted fork. This feature is particularly important when the fork assembly includes disk brake means having a brake disk on the wheel hub that cooperates with brake pads mounted on the adjacent fork leg.
A further object of the invention is to provide an axle having a first end that is enlarged and non-circular in cross section, an intermediate portion that has a uniform-cylindrical outer circumference upon which the wheel hub is rotationally mounted, and a second non-circular end portion of smaller cross-sectional area than the cylindrical intermediate portion. In this manner, during assembly, the axle smaller end may be introduced, in succession, through a first dropout opening, the bore of the wheel hub, and finally into the second dropout opening, whereupon the dimensions of the dropout openings are reduced to clamp the fork leg portions to the non-circular axle ends, respectively.